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### Question: How to know you have Fragile X syndrome?
### Response: The diagnosis of Fragile X Syndrome is based upon detection of an alteration in the fragile X mental retardation 1 (FMR1) gene. Clinically, mentally retarded child with family history of Fragile X syndrome (especially a male relative) have higher chance of inheriting the disease. There are very few outward signs of Fragile X syndrome in babies. Babies may have a large head circumference. Measurement of oversized testes in males who have reached puberty may also suggest the diagnosis. An experienced geneticist may note subtle differences in facial characteristics. Mental retardation is the hallmark of this condition and, in females, this may be the only sign of the disease. A specific genetic test called polymerase chain reaction (PCR) is used to diagnose this disease. This test looks for an expanded mutation (called a triplet repea t) in the FMR1 gene.